Silicon-based technologies have long been the dominant driver of modern microelectronics. In the decades since the first rudimentary silicon electronic devices were demonstrated, continuing advances have resulted in ever smaller, faster, and more highly integrated components and circuits.
More recently, photonic technology, in which information is carried via optical rather than electronic signals, has matured as a technology for transmission of information, particularly in the form of long-haul optical fibre communications systems. A basic photonic system includes a light source (e.g. a laser), a modulator for impressing information upon an optical signal, a waveguide, and a photodetector. However, in contrast to silicon electronics, where all components can be integrated onto a single chip, current generation photonic systems are mainly based on discrete components and serial fabrication. There has long been a desire to transfer the benefits of mature silicon fabrication technology into the field of photonics, including the development of integrated circuits combining both photonic and electronic components. Optical transmission can achieve much higher data rates than metallic conductors, without creating problems associated with electromagnetic interference. Integrated photonic/electronic circuits could therefore provide new functionality, along with faster communication between circuit boards, chips on a board, and even between different elements on a single chip.
Silicon photonic technologies could also be useful to provide optical processing functions in optical communications systems, such as switching, filtering, and wavelength-based processing, such as multiplexing and demultiplexing of optical channels. Applications of photonic circuits may also be found in the field of sensing.
In addition to the availability of mature fabrication processes, silicon itself has a number of desirable physical properties. For example, silicon has a high thermal conductivity and a high optical damage threshold, and is therefore an advantageous choice of material for photonic applications. Silicon-on-insulator (SOI) wafers are available at relatively low cost, and high quality, providing the promise of efficient and cost-effective fabrication of CMOS-compatible planar lightwave circuits.
Similar considerations apply to other established technologies and materials, such as silicon nitride (Si3N4), semiconductor materials such as InP and other III-V semiconductors, and high-index glasses, such as chalcogenide and tellurite glasses.
A key element in a wide range of optical circuit applications is a resonator. Resonators can be used in a range of applications, such as wavelength filtering, dispersion engineering, and field enhancement.
There is, accordingly, a continuing demand for the development of new resonant structures that can be efficiently fabricated in SOI technology, which are compact, and which can be employed in a range of optical and opto-electronic signal processing, communications, sensing, and other applications. Embodiments of the present invention provide a range of novel devices that address these requirements.